Powdered catalyst recovery



Aug. 3l, 1943. R. E BUTIKOFER POWDERED CATALYST RECOVERY Filed June 29, 1940 Patented Aug. 31, 1943 UNITED STATES PATENTv FFICE POWDERED cA'rALYsT RECOVERY Robert E. Butikofer, chicago, nl., assignbi- 'to v Standard Oil Company, Chicago,

ration of Indiana Ill., a. corpo- Appucation June 29, 1940, ser'iaINo. l343,151

(ci. 19a-52) Claims.

This invention relates to catalyst recovery and it pertains more particularly to the removal ofV powdered catalyst from hot vapor -streams. y

Many hydrocarbon conversion processes, such as catalytic cracking, catalytic reforming, catalytic.isomerization, etc. employ powdered catalyst which is contacted with hydrocarbon vapors at high temperatures in a reaction zone, then separated from the hydrocarbon vapors, regenerated and returned to the contacting step. such processes considerable troublehas been experienced in removing particles of catalyst from Vconversion processes but is applicable to other systems wherein it is desired to remove finely temperature that a partial condensation of the I 1 hot hydrocarbon vapors is eected. Alternativethe hot hydrocarbon vapors. Most of the catalyst can be separated from said vapors by centrifugal separation in the so-called cyclone separators but a small amount of catalyst is usually l.carried with the gases and vapors leaving such separators and entering the hydrocarbon fractionator towers. The residual catalyst then settles out on the bubble trays inthe fractionating towers and impairs the quality of the residual oilleavingvsuch towers and increases the difilculty of fractionation. It hasbeen proposed to partially condense the 'hydrocarbon vapors in a heat exchanger and to recycle the condensate -to'- gether with the catalyst which accumulates therein to the hydrocarbon conversion step but heat exchangers are likewise plugged by accumulated catalyst matcial. Furthermore, in many processes it is undesirable to recyclea very large amc 'nt of heavy condensate because such mathe subsequent conversion step.

' An object of my invention is to avoid the use of heat exchangers for cooling gases andvvapors containing powdered catalyst material and to efterial may impair the activity of the catalyst in fect the separation of all of the catalyst from said i gases and vapors before they are introduced into the fractionating tower.

A further object is to provide an improved method and means for weighting the extremely fine catalyst particles so that they can be removed substantially completely by simple centrifugal means. Even the loss of .1% of catalyst in the separation system may require many tons of catalyst per day in a commercial plant, and complete catalyst separation is therefore a mat-` ter of great importance.

A further object is to provide an improved system for employing gas oil as a scrubbing means for removing powdered catalyst from hot hydrocarbon vapors and gases. Other objects will be apparent as a detailed description of the invention proceeds.

The invention is not limited to hydrocarbon 1y, the introduced liquidv may be vaporized and then partially condensed or may be introduced in amounts and at such temperatures that a resulting temperature of incipient condensation is obtainedin any case the net result is the creation of a fog or mist of condensed hydrocarbons Athe liquid particle size of which is extremely small. The condensation may be effected on the particles themselves or the particles may be wet by contact with these extremelyA small droplets so that the catalyst particles which were originally present in the vapors are transferred to be incorporated in or otherwise Weighted'by the small liquid droplets which are thereafter suspended in the vapors. This mist or fog with its contained solid particles is then separated from the remaining gas and vapors by simple centrifugal separation, the heavier liquid droplets respending to centrifugal action which-would -be ineffective for the lighter solid particles.

The introduced liquid may be called a scrubbing liquid although my Vinvention does not operate inthe manner of conventional scrubbers. This scrubbing liquid 'may be introduced into the hot gases before the gases are introduced into the wet centrifugal separator or the scrubbing liquid may be introduced directly into the wet centrifugal separator.V Preferably, this scrubbing liquid, in the case of catalytic cracking, is a gas oil which may be a part or all of the gas oil charging stock or which is preferably a cooled gas oil or heavy lnaphtha fraction separated from the system and which is effectively recycled within the system itself. The small amount of liquid which is-withdrawn from the wet centrifugal separator and which contains the powdered catalyst material, may be returned for introduction with fresh charging stock.

The invention will be more'clearly understood from the following detailed description read in conjunction with the accompanying drawing wherein I have diagrammatically illustrated a flow sheet of a catalytic cracking process empl'oying my invention.

Gas oil charging stock from lines II) or Il or from both lines is introduced into line I2 into which line powdered catalyst may be injected from storage hopper I3 and line I4, by a suitable device such as pressure screw feeder exemplied by the Fuller-Kenyon pump. The powdered catalyst may be of the activated clay type or the synthetic type and for lcatalytic cracking it is preferably an activated hydrosilicate of alumina. No novelty is claimed in the catalyst per se and further description is therefore unnecessary. The nature of the catalyst will vary for different processes-for aromatization or-'reforming (hythrough lines 21 and 28 and 29a, b and c into the v hot gases in line 24 which are en route to wet centrifugal separator 30. The gas oil charging dro forming) it may be activated alumina with molybdenum oxide or chromium oxide deposited thereon. In any case the particle size will be small and may range from 200 to 10 microns or even smaller in diameter.

The mixture of powdered cracking catalyst and gas oil passes through coils I5 of a pipe still furnace wherein the gas oil is heated to a temperature of about 850 -to 1050 F. under pressure which may range from atmospheric to 50 pounds or more per square inch. Preferably the powdered catalystis added by line I4a to the superheated gas oil vapors leaving the pipe still furnace through transfer line I6 instead of being introduced with the charging stock. The addiy tion of the regeneratedcatalyst directly to the superheated gas oil vapors in transfer line IGI accomplishes many important advantages. It avoids the severe erosion in pipe still coils 'that would result if all of this catalyst were passed therethrough. It avoids the undue cooling of the catalyst and wetting of the catalyst with liquid oil. The regenerated catalyst may be at a higher temperature than the temperature of vapors leaving the pipe still coil and they may thus supply the last increment of heat required for effecting the conversion. The small amount of spent catalyst which is recycled to the pipe still coils in the manner hereinafter described has been found to be adequate for keeping the pipe still coils free from coke deposits.

The hot hydrocarbon vapors, carrying the powdered catalyst in suspension, pass from transfer line I6 through reaction conduit I1 which is of such size and length that a reaction time of abou 1 to 50 seconds is provided. The amount of catalyst and time of contact vary with different processes and charging stocks but I prefer to employ about 0.2 to pounds of catalyst per pound of oil employed.

Hot reaction products from conduit I1 are introduced into the upper part of cyclone separator I8 which is provi'ded with a central cylindrical baille I9. Under properly controlled conditions about 99% to 99.9% of the catalyst is separated from the vapors in this cyclone separator, the separated catalyst passing downwardly into stripping tower 20 into the base of which a stripper gas, which may be normally gaseous hydrocarbons produced in the system, steam or any inert gas, is introduced through line 2l. 'Ihe stripper gas is introduced at such a rate that it will not impede theA downward flow of the catalyst over inclined bafiles 22 but will remove the adsorbed oil therefrom. Enriched stripper gas is withdrawn through line 23 to line 24 thro`ugh which gases are withdrawn from the top of the cyclone separator.

In practicing my invention I may introduce fresh charging stock from line 25 by pump 26 stock so introduced into line 24 is proportioned in amounts and controlled as to temperatures so that its vaporization will lower the temperature of the hot reaction products to the incipient condensing temperature of the heaviest fractions of said products. In other words, I effect a cooling of these hot gases and vapors by the vaporization'of gas oil therein instead of by using heat exchangers and in this manner I overcome plugging problems and the fouling of heat exchange surfaces.V When gas oil is introduced in such amounts and at such temperatures the highest boiling components of the gas oil and of the reaction products will tend to condense in minute droplets to form a fog or mist. These droplets may condense on the particles of catalyst or they may impingeV against particles of catalyst but in any event the remaining catalyst particles in the vapor stream are soon occluded in or wet by these small liquid droplets. l

The gas vapor stream containing the mist or fog of liquid droplets is then introduced tangentially into the lower part of wet centrifugalseparator at such velocity that the centrifugal force of the swirling gases will be sufficient to throw thev liquid droplets to the walls of the separator. lThus a small amount of the liquid which has heretofore been condensed runs down the sides of the centrifugal separator carrying with it al1 of.' the solid catalyst particles and this liquid stream together with catalyst material may f it is preferably a verticalelement provided with a plurality of atornizing nozzles so directed as to augmenty the centrifugal swirling motion of the gases which are tangentially introduced at the base of the separator and which are finally withdrawn from the top of the separator through line 36 to fractionating tower 31. The same prinlciple is applicable in this case as has been heretofore described-the amount of gas oil introduced through atomizer should be suiilcient to effect by its vaporizationa lowering of the temperature in this separator to such an extent as to cause the formation of a heavy gas oil mist which picks upltheparticles of powdered catalyst and carries those particles to the walls of the separator. l

'I'o prevent pasty solids from adhering to the walls of separator 30 I provide scrubbing means, preferably in the form of an annular pipe 35 having perforations directed against the inner walls of tank 30. Scrubbing liquid may be introduced into pipe 35' through line 34'. Any num; ber of annular scrubbers of this type may be used or any equivalent means employed to insure the removal of solids thrown out of the vapor stream in separator 30.

From fractionating column 31 gases mayl be I taken overhead through line 38, cooled in cooler 39 and introduced into separator 40 from which une n. A portion of these liquids which may be chiefly propane, butane or a mixture thereof may be withdrawn from the system throughA line 43 and 'another portion returned by pump 44 through 'line 45 for use as reflux in the top of tower 31. Cracked gasoline may be withdrawn as aside stream through line 46. forms no part of my invention and is therefore shown in simple diagrammatic form. Actually I prefer to take end point gasoline from the top 'of tower 31 and to stabilize the gasoline in a separate tower.

A reboiler 41 in the base of tower 31 insures the removal of gasoline hydrocarbons from the gas oil which is withdrawn from the base of this tower The stripper gas for column 33 may be hot flue'gas, steam, orany inert gas which is suitable f for lremoving the oxygen-containing gases from The fraction system through line 4B. This gas oil may be passed by f pump 4b throgh lines Wand ilv through cooler 52 and line 53vto atomizer 3l for use as a scrubber liquid in wet centrifugal separator 33. Al-

ternatively, it may be withdrawn through line I4 the powdered catalyst. Such stripper gases are introduced through line 10 and withdrawn through line 1l. These gases together with regeneration gases from cyclone separator 64 are passed through line 12 and-heat transfer means 13 which may be a waste heat boiler or anyother device for utilizing the heat contained in these regeneration gases.

While I have described in detail a preferred Vembodimentof my invention it should be understood that I do not limit myself to the use of gas oil as a scrubbing liquid since any liquid may be used which will not interfere with the process ln,

which the invention is used. Wherever I have -shown a single cyclone separator it should be to line 33 for recycling to line vI2 or it may be withdrawn from the system through line 35. My preferred scrubbing liquid is a lighter gas oil fraction which is withdrawn as a side stream from fractionating tower 31 through line 5I and which is passed by pump 51 through lines B3 and 5I, cooler 52, line 53' and ',line 34 toV atornizer or distributor 35, The gasoil thus removed as a side stream does not require as much cooling as the gas oil removed from the bottomof tower 31 and is in general a cleaner and more desirable scrubbing liquid forremoving the suspended catalyst particles from the vapor stream. Practi-` cally speaking, this gas oil flows in a continuous cycle from fractionating tower 31 to centrifugal separator 30 and then back to lfracti'onating tower 31, only a very small part of the gas oil actually condensing in the centrifugal separator. One

of the features of my invention is the extremely small amount of liquid which has to be returned through lines 3|, 33 and I I to carry the separated lcatalyst back to the heating -coils the amount of this liquid being only about 5to 20% of the total gas oil resulting from the process.

When gas oil charging stock is employed as a scrubbing liquid and introduced through either -lines -28' or 34, then this charging stock is introduced into the coils of the pipe still chiefly through lines 54, 33 and il although 'a small amount of the gas oil will find its way back j through lines 3l, 33 and `I I. When the scrubbing liquid is obtained from side draw-off line I3 all of the gas oil charging stock may be introduced into line vi2 through line I0 and in this case it j may be desirable to withdraw the cracked gas oil from the system through line il instead of recycling it. If charging stock is usejdas a scrubbing liquid it should be higher boiling than gasoline so that it may be separated from the gasoline in tower 31 and passed to the cracking step.

understood that a plurality of such separators may be used. Other embodiments and modifications of the invention will be apparent to those skilled in the art from. the above description of my preferred embodiment.

Iclaim:

1.y `The method of separating powdered catalyst from hydrocarbon conversion products which comprises introducing a mixture of hot hydrocarbon conversion products and powdered catalyst into a dry separation zone, separating about 95 to 99.9% of said catalystv from said gases and vapors in said dry separation zone, injecting liquid gas oil into the gases and vapors leaving said dry separation zone, the amount and temperature o f said gas oil being regulated to reduce the temperature of the hydrocarbon gases and vapors to the incipient condensation temperature of the heaviest constituents thereof whereby a mist of liquid droplets is formed in said stream for 1 weighting the solid catalyst particles, subjecting said mist to centrifugal force in a catalyst separation zone for separating the liquid particles from the gases and vapors, withdrawing liquids together with substantially all of the solids from the base of said last-named separation zone, and

.introducing gases and vapors from the top of said last-named separation zone into a fractionation zone at an intermediate point therein.

2. Themethod of removing powdered catalyst from hot hydrocarbon conversion gases and of preventing catalyst from entering a fractionation zone which comprises introducing said hot hydrocarbon gases and vapors tangentially at the lbase of a circular separation zone whereby a swirling motion is obtained, introducing gas oil into said swirling gases and vapors-in amounts sufficient to lower the temperature thereof to the incipientcondensation temperature of the heaviest reaction productsltherein whereby a mist of very small liquid droplets is produced in the lli) ' I'he bulk of the catalyst, usually about 99% to f y 99.9% thereof, is withdrawn from the stripper column 20 through line 53 and introduced by means of va Fuller-Kenyon screw pump or other suitable means into regenerating conduit 39 into which air or other regenerationk gases may be gases in cyclone separator 34, the catalyst passing downwardly through stripping column Il and line 83 to return line 31. A pneumatic conveyor to hopper i3 from which conveyor gases'may be vented through line 33.

introduced through vlines 3|,"32 and 33. The regenerated catalyst is separated from regeneration l gas may be introduced through line 33 for conveying the regenerated and stripped catalyst back rating most4 of the catalyst from lthe hot hydrocar-bons in said zone, then cooling the hydrocarbons by' the direct injection thereinto of a vaporizabie liquid and subsequently separating the remaining catalyst from said hot hydrocarbon gases and vapors by wet centrifugal separation.

4. The method of claim 3 wherein the wet centrifugal separation is eifectedby introducing gas oil into the hot hydrocarbon stream from which most of the catalyst has already been removed, regulating the amounts of introduced gas oil to producea mist of liquid droplets, whereby the catalyst particles are transferred from said gases to said mist and subjecting said mist to centrifugal action for the separation of liquid droplets from hydrocarbon gases and vapors.

5. The method of separating residual powdered catalyst material from hot hydrocarbon vapors which comprises cooling said vapors to a temperature of incipient condensation and tangentially introducing said cooled vapors into a centrifugal separator in order to effect a swirling motion of said vapors in said separator, introducing a liquid hydrocarbon mist into said swirling vapors wherebyr the solid catalyst particles are weighted by contact with the liquid droplets of said mist and condensed vapors and maintaining a sufficient swirling velocity of said vapors in said separator to separate said mist andcondensed vapors together` with catalyst particles from the gases leaving said separator whereby the vapors leaving said separator are substantially denuded from catalyst particles before they enter a fractionation zone.

6. The method of claim 5 wherein the cooling of said vapors is eiected by introducing a vaporizable hydrocarbon liquid into the vapor stream before said stream enters said separation zone.

7. The method of claim 5 wherein the'vapors are sufficiently cooled before they enter the separation zone to prevent appreciable vaporization of liquid in said separation zone,

8. The method of operating a powdered cata.- lyst system for the conversion of hydrocarbon oil charging stocks into motor fuel which method comprises vaporizing said charging stocks in pipe still coils and contacting said charging stock vapors with powdered catalyst suspended in a stream of said charging stock vapors in a reaction zone maintained at conversion temperature, separating about 99% to 99.9% spent catalyst from said stream, stripping hydrocarbons vfrom the separated catalyst, suspending the stripped catalyst in a regeneration gas stream, regenerating said catalyst, returning said regenerated catalyst for suspension in further amounts of vaporized charging stock, commingling with incoming liquid charging stock the hot stream of vapors from the reaction zone after the approximately 99% to 99.9% of the spent catalyst has been separated therefrom, employing a suiciently low temperature in the commingling step to partially condense the vapor stream and pick up the bulk of v the remaining unseparated spent catalyst in said incoming,charging stock to form a slurry before said charging stock passes through said pipe still system for the conversion of hydrocarbon oil charging stocks which method comprises contacting hydrocarbon oil charging stock vapors with powdered catalyst in a reaction zone while maintaining powdered catalyst suspended in a stream of said vapors, separating at least about 99% of the spent catalyst from said Vapor stream in a dryY separation zone, separating the bulk of the remainder of the spent catalyst from said stream in a subsequent wet separation zone by contacting it with liquid charging stock at a temperature sufliciently low to condense the higher boiling components of said vapor stream whereby at least about .1% but less than 1% of the total spent catalyst is added to said charging stock, heating said charging stock to conversion temperature in pipe still vcoils in the presence of said added spent catalyst, stripping and regenerating spent catalyst separated in said dry separation zone and contacting said regenerated catalyst with said hydrocarbon oil charging stock after it has been heated to conversion temperature in the presence of said spent catalyst separated in said wet separation zone.

10. The method of catalytically cracking a hydrocarbon charging stock by means of powdered catalyst having a particle size below 200 microns which method comprises heating said charging stock in a confined stream to a temperature ofv about 850 to 1050 F. whereby said charging stock is vaporized and brought substantially to conversion temperature, suspending in said charging stock vapors about .2 to 20 pounds of powdered catalyst per pound of oil employed and introducing said suspended catalyst by means of said charging stockl vapors into a reaction zone, contacting said vapors with said catalyst in said reaction zone for a period of time exceeding one second but not exceeding fifty seconds, separatingabout 99 to 99.9% of the catalyst from contacted vapors in a dry separation zone, then separating the remaining about 1 to .1% of the catalyst from the contacted vapors in a wet separation zone by commingling said vapors with liquid charging stock at a temperature sufciently low to condense the higher boiling components of said contacted vapors whereby the remaining .catalyst particles are picked up in charging stock, effecting the heating of the charging stock in the presence ofthe catalyst picked up in the wet contacting zone, stripping and 'regenerating the catalyst separated in the dry separation zone and resuspending said regenerated catalyst in vaporized charging stock subsequentY to said heating step.

ROBERT E.` BUTIKOFER. 

